Trenching machines of the type having a multiplicity of buckets circumferentially arranged about a digging wheel often employ rotatable rock type bits, wherein the rotatable bits are removably received within a pocket made especially therefor. The pocket usually is welded to the bucket lip. The rock bit is made for digging in hard, rocky formations and for this reason, it is rotatably received within the bore of the pocket, so that as the formation is engaged by the forward end of the bit, the bit rotates within the pocket, thereby promoting even wear about the wear surfaces thereof.
From time to time, the formation encountered by the trencher will change from rock to soil or clay, and when this change in the formation characteristics occur, it is advantageous to employ a non-rotatable, blade-like digging tooth in lieu of the rotatable rock bit. The pocket for the rock bit is usually quite different from the pocket required for the blade-like tooth, and it is therefore unfeasible under ordinary circumstances to change the pockets on the bucket lip so that the pocket will receive an ordinary blade type digging tooth.
College, et al U.S. Pat. Nos. 4,346,934; Taylor, et al 4,316,636; and Swisher, Jr., et al 4,335,921 set forth means for rendering digging teeth non-rotatable respective to the tooth receiving pocket thereof.
Swisher, Jr., et al, in FIGS. 1 and 2, forms a support block shoulder 54 which engages a shoulder 74 formed on the rear end of the tooth shank. FIGS. 4 and 5 thereof illustrate a yoke 140 secured within a channel 138. Other figures of the Swisher, Jr., et al drawings illustrate a yoke which mates with a support block shoulder formed on a face of the support block.
Taylor, et al discloses a bit shank of non-circular configuration received within a complementary bore of the support block, while College, et al discloses a digging tooth having a shank 24 received within a bit block 36. A tang 38 extends into abutting contact with a face of the bit block and prevents rotation of the digging tooth respective to the bit block.
When excavating relatively soft formation, the digging teeth of Swisher, Jr., et al and Taylor, et al cause the excavated material to wear against critical areas of the bit block or pocket and ultimately the bit pocket is eroded away and either must be rebuilt or replaced. This is an expensive endeavor and necessitates substitution of a new block for the old, which naturally requires that the old block be cut off with an oxy-acetylene cutting torch and then the resultant irregular surface must be dressed down by grinding or the like, so that the new block can be welded in its place. Alternatively, the old block must be build up with welding, which results in the continued use of a pocket having considerable wear in the bore thereof. In both Swisher, Jr., et al and Taylor, et al, the bore formed in the bit block has been modified considerably. The Taylor, et al block will no longer accept a circular shank of a rock type tooth.
College, et al relies upon the tang 38 extending down the forward face of the bit block in order to prevent tooth rotation, and accordingly, when a rotational force is effected on the bit, the tang 38, if rotated respective to the block, presents a mechanical advantage which thrusts the shank 24 in an outward direction respective to the block bore.
It would therefore be desirable to have made available an improved digging tooth having a shank which is circular in crosssection and is easily mounted within a rock bit type pocket; and wherein a digging tooth of the type which efficiently digs in a soft formation can be non-rotatably mounted therein by the provision of a rearwardly directed shield having opposed wall surfaces formed thereon for engaging opposed wall surfaces of the bit receiving pocket. The advantages of this novel construction are the presentation of a digging tooth which can be used in conjunction with a rock bit type pocket, wherein each tooth is rendered nonrotatable by capturing the outer sidewalls of the rock bit pocket within a cavity formed by the inner walls of the shield. The improved dirt digging tooth protects the bit pocket from wear; and, during the digging operation, the tooth shank is forced more securely into the bore of the pocket.
Throughout this disclosure, the term "bit" is intended to denote a rotatable type digging implement such as a rock type bit, while the term "tooth" or "teeth" denotes a non-rotatable type digging implement. The invention described herein is for use on trenchers having a plurality of buckets mounted to a circular wheel, as well as the endless chain type trenchers, and further includes buckets such as may be found on hydraulic excavators.